1. Field of the Invention
The present invention relates to a cross-flow type microchannel apparatus for producing and separating emulsions used in the food industry, manufacturing of drugs and cosmetics, etc. and to a method of producing and separating emulsions making use thereof.
2. Description of Related Art
Techniques in which a biphasic system for which a separated state is thermodynamically stable, such as that composed of a water phase and an organic phase which are emulsified to obtain a semi-stable emulsion, are conventionally known. As general emulsification methods, there have been described in "Science of Emulsions" (Asakura-shoten, 1971), the methods using a mixer, a colloid mill, a homogenizer, etc., and the method of dispersion with sound waves, which are all well-known.
The general methods mentioned above have a disadvantage in that diameters of dispersed phase particles in a continuous phase are distributed over a wide range.
Therefore, a method of using filtration through a membrane comprising polycarbonate (Biochemica et Biophysica Acta, 557 (1979), North Holland Biochemical Press); a method using repeated filtrations through a PTFE (polytetrafluoroethylene) membrane (Proceedings of the 26th Autumn Meeting of the Society of Chemical Engineers, Japan, 1993); and, a method of manufacturing homogenous emulsions by transferring a dispersed phase into a continuous phase through a porous glass membrane having uniform pores (Japanese Patent Application Laid-Open No. 2-95433), have been proposed.
As a method of producing emulsions using a nozzle or a porous plate, a laminar-flow dripping method (KAGAKU KOGAKU Vol. 21, No. 4, 1957) is also known.
The method using filtration through a membrane comprising polycarbonate and the method using repeated filtrations through a PTFE membrane theoretically cannot manufacture emulsions of particles larger than the membrane pores and cannot separate particles smaller than the membrane pores. These methods are therefore especially unsuitable for producing emulsions of large particles.
In the method using a porous glass membrane having uniform pores, when the average diameter of the membrane pores is small, particle diameters are distributed in a narrow range and thus homogenous emulsions can be obtained. When the average diameter of the membrane pores is increased, however, particle diameters become distributed over a wide range so that homogenous emulsions cannot be obtained.
In addition, in the laminar-flow dripping method, particle sizes become 1,000 .mu.m or more and are distributed over a wide range so that homogenous emulsions cannot be obtained.
Therefore, the inventors of the present invention formerly proposed an apparatus for producing emulsions which can solve the above-mentioned problems and disadvantages of the known methods in Japanese Patent Application Laid-Open No. 9-225291.
As shown in FIG. 10, in this apparatus, a supply port 101 for a dispersed phase is formed in a center part of a base 100, a gap 103 to which the dispersed phase is supplied is formed between the base 100 and a plate 102 placed opposite the base 100, a large number of microchannels 104 having a predetermined width are formed in a boundary section between the dispersed phase and a continuous phase, the dispersed phase is brought into contact with the continuous phase via the microchannels 104, and the pressurized dispersed phase is mixed into the continuous phase as microspheres and obtained emulsions are withdrawn from a withdrawal ports 105.
In the apparatus disclosed in Japanese Patent Application Laid-Open No. 9-225291, the dispersed phase is spread from the supply port 101 formed in the center part of the base to the microchannels 104 formed to surround this supply port. Therefore, it is necessary to apply considerably high pressure to the supply port 101 in order to obtain sufficient pressure to obtain break-through at the microchannels.
In order to improve this problem, the inventors of the present invention have proposed an apparatus for withdrawing emulsions by using differences in specific gravity (differences in density) and floating emulsions. This apparatus is workable when the difference in specific gravities is sufficiently large, however, it cannot withdraw emulsions effectively when the difference in specific gravities is small.
On the other hand, in the case of separating emulsions by using the apparatus disclosed in Japanese Patent Application Laid-Open No. 9-225291, if emulsions are supplied from the supply port 101 formed in the center part of the base and the continuous phase is withdrawn via the microchannels 104, there is a block created at the inside part of the microchannels by the dispersed phase for a short time. Conversely, if emulsions are supplied to the outside region of the microchannels, a block is created at the outside part of the microchannels of the dispersed phase for a short time.